There has been known check valves which allow fluid, such as water in a piping, to flow unidirectionally in a specific direction. The check valves are classified by operational modes of the valve discs into various types. It is difficult for swing-type and tilted-disc (butterfly) check valves, having the valve discs which open obliquely to the valve seats, to quickly close the valve discs, causing water hammer. On the other hand, the lift-type check valves including those of Smolensky type, are capable of swiftly closing the valve discs, since the valve discs oscillate in a linearly reciprocating manner in the direction they approach or depart from the valve seat, and thereby water hammer is avoidable in an effective manner.
Patent Literature 1 describes a straight lift-type check valve. This check valve is a straight valve in which the inflow direction towards the body and the outflow direction agree, so that the axial flow direction, given by connecting the inflow direction and the outflow direction, is straight. When pressure difference between the primary side and the secondary side of the valve disc exceeds a predetermined minimum working pressure (cracking pressure), the valve disc lifts up from the valve seat so as to allow the fluid to flow therethrough. The flow path of fluid, before and after the passage through the valve seat, is orthogonal to the axial flow direction, and is bent inside the body.
Patent Literature 2 describes a lift-type angle check valve. This check valve is an angle valve having the inflow direction towards the body orthogonal to the flowout direction, wherein the axial flow direction connecting the inflow direction and the flowout direction is bent inside the body. When pressure difference between the primary side and the secondary side of the valve disc exceeds the cracking pressure, the valve disc lifts up from the valve seat so as to allow the fluid to flow therethrough. The fluid which passed the valve seat collides on the valve disc to bend the flow path, and then discharged out from the body.